Cornwall has been a relatively isolated part of the British isles. Up to 1550 it spoke its own language, and had its own form of government and currency until the 1700s. Compared with other parts of Britain there has been relatively little intermingling, except perhaps for Devon and with Brittany. Around 800 AD, a large group of Irish missionaries arrived, but apart from the odd Anglo-Norman lord, there has been limited in-migration until the present century. After 1850 however, when the great mines began to play out, there was a major exodus to other parts of the world where mines were to be found (Australasia, North and South America, South Africa)
We believe that the unique features of Cornwall will be reflected in the Y-DNA distribution, which we expect to be different to that of Britain in general.
At this stage we accept only men with a paternal family tree (and usually a surname) with Cornish origins pre-1900. A good paper tree on the male line leading to Cornwall
Examples of surnames are anything beginning with Tre-, Pen- or Kil-, ending in -kin or -o, and many patronymics such as JOHN, GILBERT, PHILIPS etc. A partial list is at http://www.jimwearne.com/Cornish_Names.htm
and also here